Information on the drug paxil

Paroxetine (Paxil®):

Information On The Drug Paxil Studies
In general, paroxetine has shown superior efficacy compared to placebo and equal efficacy to TCAs and other SSRIs in the treatment of depression. Trials comparing paroxetine and TCAs have found similar efficacy (50 to 70 percent response) but better tolerability with paroxetine.

Paroxetine hydrochloride is a phenylpiperidine antidepressant structurally unrelated to other available antidepressants, including other selective serotonin reuptake inhibitors (SSRIs).

Paxil was approved for use in the United States in 1992. SSRIs have surpassed tricyclic antidepressants (TCAs) as first-line therapy for the treatment of major depression. Numerous clinical trials in patients with depression have shown the SSRIs to be equivalent to TCAs in efficacy, but superior in tolerability and safety.

Indications
Paroxetine is indicated for the treatment of depression, obsessive-compulsive disorder and panic disorder.

How Paroxetine works:
The mechanism of action of paroxetine (Paxil) is serotonin (5HT) reuptake blockade via inhibition of the serotonin reuptake transporter. Blockade of this transporter initially leads to increased concentrations of 5HT in the synaptic cleft. In response to increased 5HT, 5HT1A autoreceptors act to decrease serotonin neurotransmission (auto-feedback mechanism).

Paroxetine's inhibitory effects on the reuptake of norepinephrine and dopamine are minimal. Of the available SSRIs, paroxetine is the most
potent inhibitor of 5HT reuptake. Paroxetine is more selective for serotonin (vs. norepinephrine) reuptake inhibition compared to fluvoxamine, sertraline, and fluoxetine. Paroxetine has negligible affinity for adrenergic, dopamine D2, histamine H1, and 5HT2 receptors and weak affinity for muscarinic cholinergic receptors.

Pharmacokinetics (The process by which the Paxil is absorbed, distributed, metabolized, and eliminated by the body)

Drug Paxil is well absorbed from the gastrointestinal tract after oral administration. It undergoes extensive first-pass metabolism (partially saturable), estimated to be approximately 50 percent. Due to its highly lipophilic properties, paroxetine distributes widely in tissues including the central nervous system, with only one percent of the drug remaining in
the systemic circulation.

Paroxetine (drug Paxil) distributes into breast milk, with concentrations similar to those found in plasma. Advanced age and severe renal or hepatic impairment have been associated with increased paroxetine half-life and serum concentrations. Paroxetine is extensively metabolized in the liver by oxidation and methylation. Its glucuronide and sulfate metabolites are not pharmacologically active.

Paroxetine is also partially metabolized by the cytochrome P450 (CYP) CYP2D6 isoenzyme. Saturation of this enzymatic pathway appears to account for the non-linearity of paroxetine's pharmacokinetics at high doses.

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About SSRI Antidepressants